Over the past few decades there has been a significant increase in the number of new systems for conversion of solar energy and/or wind energy into electricity. Many such systems first a) convert the solar/wind energy into DC electricity and thereafter b) convert the DC electricity into AC electricity for feeding into an AC power grid and for any other needs, such as UPS, CARS, etc.
A regular prior art P.W.M converter works in this way, for example: for zero output level, the duty cycle is 50%—half the time it is charging and half the time it is discharging, which causes a waste of energy.
A capacitor is charged and discharged all the time, at the frequency of the modulator switching carrier wave, to produce 50 or 60 Hertz sinusoidal output wave voltage, for example, to create a zero output frequency level in a regular PWM 50 percent high without, and 50 percent low load and the switching losses are relatively high in a regular P.W.M or PM modulation.
The second disadvantage of the prior art is the cross conductivity, when one switch is on and the other is not yet completely off. The prior art solution is a dead time and is also reducing the efficiency.
Some patent publications in the field include:
U.S. Pat. No. 4,488,057 describes a power supply for a load such as a computer, which is sensitive to power interruptions. A switching regulator is coupled to both the AC power line and a rechargeable battery, and makes automatic transitions between AC operation and battery operation, utilizing a transistor switch and an energy storage transformer coupled to both power sources and to the load. The transistor switch is driven by a variable duty cycle control signal provided by a programmed current feedback circuit responsive to both output voltage and instantaneous switch current. The feedback circuit cuts off the switch each time the peak current through the switch reaches a value corresponding to the desired output voltage, thus improving control-loop stability and maintaining a constant peak current through the switch to substantially eliminate ripple. The circuit enables one terminal of the battery to be connected to one terminal of the switching transistor, to minimize noise. A charging circuit recharges the battery whenever the AC power line is operating within normal limits.
U.S. Pat. No. 4,560,886 discloses an alternating current power source which controls its own alternating current output through a feedback circuit which monitors the alternating current output. The power source can be used as a backup to a primary power supply which provides power to a load. The invention described in this patent includes embodiments with dual independent source circuits which continuously monitor such primary power supply to detect power interruptions in the primary power supply. When an interruption is detected, monitoring logic circuitry of the alternating current power source disconnects the primary power supply from the load and energizes line driver circuitry of the present invention which provides the alternating current output. When the power interruption ceases, the monitoring logic circuitry reconnects the primary power supply to the load and disables the line driver circuitry so that alternating current is not provided by the present invention to the load. The alternating current power source includes an internal power supply which can be recharged through the line driver circuitry by the primary power supply when there is no power interruption in the primary power supply.
U.S. Pat. No. 4,728,808A describes an uninterruptible power supply system having input terminals connectable to an AC power source and leading to an AC to DC converter for producing a first DC voltage source and a second DC voltage source operationally connected to the first source. The system supplying at the output of the second source a voltage normally primarily is provided by the first DC source. A capacitive accumulator device connected in parallel with a voltage sensing and controlling circuit and with the output of the two DC sources. The sensing and controlling circuit controls the output of at least the second of the DC voltage sources so as to provide at the output terminals of the system a substantially constant output voltage also when the AC power source to which the system is connected is interrupted.
Some of the problems associated with these systems include:
a) These systems have energetic power losses due to working in both charging and discharging capacitor simultaneously and continuously;
b) These systems work with two inductor coils in series and between them there may be formed a cross-conductivity leading to further energetic power losses and loss of reliability.
There is thus still a need to provide systems and methods which overcome the aforementioned problems.